A regional monitoring group says South Sudan's military has launched a full-scale military offensive despite calls for restraint.

The regional bloc known as IGAD, which has been mediating peace talks between South Sudan's warring factions, said in a statement Friday that the latest fighting is "unwarranted and appalling."

Earlier this week, the U.N. announced there were credible reports of atrocities being carried out, including killing of civilians, rape and the torching of 28 villages.

South Sudanese military spokesman Col. Philip Aguer said government troops have been ordered to pursue rebels in Jonglei state as well as south of Unity state.

The U.N. says 100,000 people have been displaced by the latest fighting in Unity State and that 500,000 needy people are without humanitarian aid.